What are the main methods used by car manufacturers to reduce emissions in their ICE cars besides trying to lower the amount of fuel the engine uses?
Some of the main methods used by car manufacturers to reduce emissions in their ICE cars besides trying to lower the amount of fuel the engine uses are:

- Using catalytic converters to reduce harmful gases such as carbon monoxide, nitrogen oxides and hydrocarbons.

- Implementing exhaust gas recirculation (EGR) systems to lower the combustion temperature and reduce nitrogen oxide emissions.

- Applying selective catalytic reduction (SCR) technology to inject urea into the exhaust stream and convert nitrogen oxides into harmless nitrogen and water.

Would you like any more information on any of these methods?
An internal combustion engine vehicle or “ICE” vehicle?
Assuming that hybrid car may not be considered, [it is semi-electric]

Ill list 10 ways for you from order of most impactful to least starting with...

#1 Catalytic converter is a device that converts harmful pollutants in the car's exhaust gas into less harmful emissions before they are released into the environment. It contains a catalyst, typically made of platinum, palladium, or rhodium, that promotes a chemical reaction to convert carbon monoxide, nitrogen oxides, and unburned hydrocarbons into carbon dioxide, nitrogen, and water vapor. By using catalytic converters in cars, car manufacturers can significantly reduce the amount of harmful pollutants that are released into the atmosphere. In fact, catalytic converters are required by law in many countries to meet emissions standards.

#2Engine downsizing: Car manufacturers reduce the size of engines while maintaining or increasing power output. Smaller engines require less fuel to run and produce fewer emissions.

#3Lightweight materials: Using lightweight materials such as aluminum, magnesium, and carbon fiber reduces the weight of the vehicle, resulting in lower fuel consumption and emissions.

#4Regenerative braking: Regenerative braking systems convert the energy lost during braking into electrical energy that is used to charge the car's battery. This reduces the amount of energy required to power the car, resulting in lower emissions.

#5Start-stop systems: Start-stop systems turn off the engine when the car is stationary and restart it when the driver presses the accelerator. This reduces the amount of fuel consumed and the emissions produced.

#6Direct fuel injection: Direct fuel injection systems inject fuel directly into the engine's combustion chamber, resulting in more complete combustion and fewer emissions.

#7Exhaust gas recirculation: Exhaust gas recirculation systems redirect a portion of the engine's exhaust gases back into the engine's combustion chamber, reducing the amount of oxygen available for combustion and thereby reducing emissions.

#8Variable valve timing: Variable valve timing systems adjust the opening and closing of the engine's valves to optimize fuel efficiency and reduce emissions.

#9Aerodynamics: Car manufacturers design vehicles with aerodynamics in mind. Vehicles with better aerodynamics require less energy to move, resulting in lower fuel consumption and emissions.

#10Eco-driving: Car manufacturers provide technologies that help drivers to drive in an eco-friendly manner, such as a gear shift indicator that tells drivers when to shift gears for optimal fuel efficiency. However, the impact of eco-driving on emissions is relatively low compared to the other methods listed.